Lower extremity peripheral arterial disease (PAD) affects 12% of men and women age 65 and older. This project will study the independent impact of PAD on lower extremity functioning and social independence among men and women age 55 and over. Specifically, the project is designed to assess whether the ankle brachial index (ABI), an accurate, reliable measure of lower extremity arterial perfusion, predicts baseline and subsequent lower extremity function. The ABI is a ratio of Doppler recorded systolic pressures in the lower and upper extremities which can be performed in clinicians' offices and is analogous to blood pressure measurement. The primary specific aims are as follow: 1) to assemble a cohort of 470 men and women with PAD and 250 men and women without PAD, all age 55 or older, and follow them prospectively for up to 38 months; 2) to define the relationship between baseline lower extremity functioning and baseline lower extremity arterial perfusion as measured by the ABI; 3) to determine the relationship between the rate of decline in lower extremity functioning over 24 months follow up and baseline lower extremity arterial perfusion as measured by the ABI; and 4) to determine whether current cigarette smoking, lack of regular exercise, diabetes mellitus, and lower physical activity levels are associated with greater functional decline among PAD subjects, independent of the ABI level. Hypotheses to be tested are as follow: 1) lower extremity arterial perfusion correlates directly and independently with lower extremity function; 2) lower extremity function among PAD subjects deteriorates at a predictable rate over time; 3) PAD subjects with a lower ABI level experience greater declines in lower extremity function over time; and 4) PAD subjects who smoke, are diabetic, do not regularly exercise, or have lower physical activity levels experience greater decrements in lower extremity function over time, independently of their ABI level. The specific aims in this study cannot be answered by the Cardiovascular Health Study, the Women's Health and Aging Study, or the Atherosclerosis Risk In the Community study. The investigators state that unique components of the proposed study include the wide spectrum of PAD severity, the large number of PAD subjects assembled, the breadth of functional assessments, and the inherent generalizability of the findings to patients routinely encountered by practicing physicians. They further state that the results of this study will be used to develop subsequent intervention studies designed to improve quality of life and prevent functional decline among men and women with PAD.